The present general inventive concept relates to the obtainment of an optical pulse using a laser diode and, more particularly, a laser diode for controlling spatial hole burning and an optical pulse generating method.
An optical pulse is used for various purposes such as clock reproduction by a reproducer in optical communication, a light source in optical communication, a light source for optical sampling, a carrier for radio-frequency (RF) communication, and so forth.
In particular, when an optical pulse is generated using a semiconductor laser diode, a device using the same has advantages in size and economical efficiency. For this reason, various researches have been conducted on a pulse laser diode.
A physical mechanism causing a laser diode to emit a pulse may be Q-switching (or gain switching), mode beating or mode locking.
The Q-switching (or gain switching) is not suitable for generating an ultrahigh-speed pulse because there is a limitation in speed for an optical output.
In case of the mode locking, a pulse is generated by increasing a reaction between oscillation modes which is achieved by inserting a nonlinear region such as a saturable absorber into a resonator. A repetition rate is determined by a distance between the modes and expressed as follows: Δv=c/(2 nL), wherein Δv represents a frequency difference between modes, c represents speed of light, n represents a group refractive index of a waveguide, and L represents a length of a resonator. Since a length of a resonator is 200 micrometers or less when a frequency of a pulse is above 300 GHz, there is a limitation in gain length. The limitation in gain length makes it difficult to construct a laser diode.
The case of the mode beating is a structure including two independent laser diode regions. An RF pulse is generated by independently selecting wavelengths of two oscillatory waves. In this case, since a distance between two modes can be adjusted arbitrarily, there is an advantage in generating an RF pulse. Unfortunately, there are many disadvantages in generating a pulse in a region of 100 GHz to 300 GHz due to the stop-band overlap of a distributed feedback (DFB) laser diode used for a single mode.
Accordingly, there is a requirement for a pulse laser having the wide frequency-adjustable range in a region of 100 GHz to 300 GHz. In addition, there may be a need for obtaining a single-mode laser diode that is efficient in use of energy by increasing an optical output in one direction.